asus-wmi: try to guess the right DSTS methods

This is tricky, new WMI aware notebooks seems to use
0x53545344 while Eee PCs are using 0x53544344. But there
is no way to know if there is an Eee PC in that wild that is
using 0x53545344 or a notebook using 0x53544344. So the
driver try to guess the available DSTS method ... But most Eee PCs
never return 0xFFFFFFFE when a method is not available, they return
0 instead (and that's useless).

So, first, try 0x53544344 then 0x53545344. We will find
a better way when we got more data.

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Matthew Garrett <mjg@redhat.com>